I would have to say that it depends on the type of client you have, and the relationship you have with that clients. I have had some where all I had to do was mention it, and it was a "go ahead and do it" no talk about money... just send a bill later on. Then you have the type of clients where you have to hold their hands. Case and point, I took a walk around a client's property with him today, showed him some things I saw and said "I just thought you should know..." Sure enough a couple hours later he called back saying I was right, and to go ahead and do the work, send him a bill once it's done. Always be planting seeds though. Phrases such as "did you ever think about...?" "wouldn't it be nice if...?" "what would you say to...?" etc.